An artist's impression of the light rail proposed to run from Civic to Gungahlin.

"We just don't know the assumptions that underpinned many of the figures put out in the public domain and we are thinking of staging a forum at the ANU in a month or so to see what we have learned," Professor Dobes said.

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"We simply don't have all the data to make judgements."

Capital Metro Minister Simon Corbell.Credit:Rohan Thomson

University of Canberra economics head of economics Phil Lewis told the newspaper an expensive light rail project might not represent sensible economic management from the ACT Government, as it manages the $1 billion Mr Fluffy asbestos buyback scheme and a deteriorating budget bottom line.

"The cost-benefit analysis that's been done hasn't been very transparent and even what we do know suggests the benefits of the project only just outweigh the costs, at best the project appears to be only marginally beneficial," Professor Lewis said.

"There have been some suggestions the project will cost at least $1 billion rather than the $700 million to $800 million so far cited and this is being imposed on a small population supporting a sizeable public debt."

The ACT opposition has also questioned Mr Corbell's statements about the possible compensation payout if a future government moves to cancel the contracts after the 2016 election.

On Wednesday, transport spokesman Alistair Coe welcomed the Victorian government's agreement to pay $339 million to get out of a controversial road tunnel project, saying it proves Canberra's light rail project could be ditched at a "reasonable" price.

Mr Corbell said it showed the Canberra Liberals could pay $340 million to exit light rail contracts. Mr Coe called the comment "bizarre" and said the government should be working to keep the costs down.

Mr Corbell told the Australian Financial Review the ACT government had been "as transparent as you can get in releasing the details of the cost-benefit analysis".

"The public is seeing the same business case that was presented to the ACT cabinet ... I don't know how we could be any more transparent."

The business case suggests a cost-benefit ratio of $1.20 for every $1 invested.

Two consortiums have been shortlisted to submit detailed bids to build, own and operate the 12 kilometre tram line, with both now preparing detailed design and final bid prices.

A final decision is expected in early 2016, and could include an extension to Russell.